Abstract. Abelisaurids are a
clade of large, bizarre predatory dinosaurs, most notable for their high, short
skulls and extremely reduced forelimbs. They were common in Gondwana during the
Cretaceous, but exceedingly rare in the Northern Hemisphere. The oldest
definitive abelisaurids so far come from the late Early Cretaceous of South
America and Africa, and the early evolutionary history of the clade is still
poorly known. Here, we report a new abelisaurid from the Middle Jurassic of
Patagonia,Eoabelisaurus mefi gen. et
sp. nov., which predates the so far oldest known secure member of this lineage
by more tan 40 Myr. The almost complete skeleton reveals the earliest
evolutionary stages of the distinctive features of abelisaurids, such as the
modification of the forelimb, which started with a reduction of the distal
elements. The find underlines the explosive radiation of theropod dinosaurs in
the Middle Jurassic and indicates an unexpected diversity of ceratosaurs at that
time. The apparent endemism of abelisauroids to southern Gondwana during
Pangean times might be due to the presence of a large, central Gondwanan
desert. This indicates that, apart from continent-scale geography, aspects such
as regional geography and climate are important to reconstruct the
biogeographical history of Mesozoic vertebrates.

Pol, D. And Rauhut, O. W. M. 2012. A Middle Jurassic abelisaurid from Patagonia and the eraly diversification of theropod dinosaurs. Proceedings of the Royal Society. doi:10.1098/rspb.2012.0660. Published online.